PROJECT SUMMARY Children and youth experience trauma at alarming rates, which can lead to serious mental health problems. Trauma-Focused Cognitive Behavioral Therapy (TF-CBT) is an evidence-based practice (EBP) for those who experience emotional or behavioral difficulties related to trauma. However, much like other EBPs, TF-CBT is underutilized, and even when organizations and systems adopt it, implementation problems can limit its effectiveness. Implementing and sustaining TF-CBT and other EBPs with fidelity may require that multiple implementation strategies be selected and tailored to address multilevel, context-specific determinants (barriers and facilitators). Ideally, the selection and tailoring of implementation strategies would be guided by theory, evidence, and input from relevant stakeholders; however, methods to guide the selection and tailoring of strategies are not well-developed. The purpose of this K01 is to partner with the SAMHSA-funded National Child Traumatic Stress Network (NCTSN) to develop and pilot the Collaborative Organizational Approach to Selecting and Tailoring Implementation Strategies (COAST-IS). The COAST-IS intervention will involve coaching organizational leaders and therapists to use Intervention Mapping to select and tailor strategies. Intervention Mapping is a multistep process that is inherently ecological and incorporates theory, evidence, and stakeholder perspectives to ensure that intervention components effectively address key determinants of change. After collaboratively developing COAST-IS in Year 1, we will conduct a randomized pilot trial of the intervention within an NCTSN learning collaborative, randomly assigning eight organizations to the learning collaborative-only condition or the learning collaborative plus COAST-IS condition. We will then evaluate COAST-IS in the following aims: 1) to assess the acceptability, appropriateness, feasibility, and utility of COAST-IS; 2) to evaluate organizational stakeholders' fidelity to the core elements of Intervention Mapping; and 3) to demonstrate the feasibility of testing COAST-IS in a larger effectiveness trial. To accomplish these aims and prepare for a larger mixed methods effectiveness trial, the applicant will receive training in 1) intervention development, 2) partnered research, 3) pragmatic randomized controlled trials, and 4) mixed methods research under the direction of Drs. Morris Weinberger, Greg Aarons, Loretta Jones, and Ken Wells. This work is significant because it will yield a systematic method that integrates theory, evidence, and stakeholder perspectives to improve the effectiveness and precision of implementation strategies. Ultimately, COAST-IS may have the potential to improve implementation and sustainment of a wide-range of EBPs in mental health and other health sectors.